Is there any documentation about what exactly the limits are on SuiteCommerce?

There is some documentation on the APC for CAP if you are a part of that. Otherwise in a nutshell you are limited to a single language and tax support for US/CA. You can't customize the core and since it is a managed bundle you will be forced to update. Advantage is that you are forced to stay-up-to-date, can get hotfixes through subversions and I believe the license is only half the price.

Thanks Kevin. Am working on the CAP program but it'll be a while. Is that doc secret info or can you send it to me? It would be nice to compare a client's requirements list to the restrictions to know if it's even a good fit for them. For example, what if I want to add a custom image gallery feature on a product page template?

The doc I was referring to is a slidedeck from the SW19 CAP session. It's only high-level and is under events in the apc CAP. Access can be arranged through Steve Butcher. Any changes to templates/scss are part of the theme and the same for SCA/SC. If you need to make js changes you will however have to create an extension with SC. The extension 'should' use the extensibility api to ensure smooth updates. It is however possible to make any change through an extension, but then it may no longer work on future versions of sca/sc... That's an issue if you are automatically updated with sc.